Communication channels are generally used to process transmitted data. Such channels are useful in a variety of applications, such as telecommunications systems and data storage devices.
In some communication channels, an input continuous (e.g., analog) signal is sampled to provide a corresponding series of discrete (e.g., digital) samples. A variety of data recovery techniques can then be applied to the-discrete samples to reconstruct the informational content of the input signal. Such recovery techniques can include partial-response, maximum likelihood (PRML) and decision-feedback equalization (DFE).
While it would appear that some informational content of the original input signal would be lost by converting the input signal to a series of discrete samples, this is not necessarily the case. The well-known Nyquist criterion generally provides that all of the informational content of a continuous signal can be recovered through sampling if the sampling rate is at least twice the highest frequency content (bandwidth) of the signal. This minimum sampling rate (twice the highest frequency) is referred to as the Nyquist rate.
By way of illustration, it is well known that the upper frequency response of the human ear is on the order of about 20 kHz; that is, humans generally cannot hear frequencies above this upper frequency threshold. Compact disc (CD) audio specifications sample original continuous audio signals at a nominal sampling rate of about 44.1 kHz, which is slightly above twice this upper frequency response (e.g., 40 kHz).
In this way, an original analog audio signal (e.g., a live performance) can be sampled at 44.1 kHz and the samples can be encoded and stored on a CD. During subsequent playback of the CD, the samples can be decoded and used to reconstruct an output analog signal that is fed to a speaker to produce a response that, to most hearers, is substantially indistinguishable from the original performance. Similar processing can be performed with other types of continuous signals such as composite video signals and transducer readback signals.
While communication channels that sample at or above the Nyquist rate have been found operable, there nevertheless remains a continued need for improvements in the art to provide channels that carry out signal processing with increased levels of performance. It is to these and other improvements that preferred embodiments of the present invention are generally directed.